A method and a device for controlling an internal combustion engine is described, for example, in the MTZ Motortechnische Zeitschrift [Engine Technology Journal] 58 (1997), no. 10, page 572 ff. The system described there is usually referred to as a common-rail system. Using the system described there, it is possible to carry out at least one first partial injection and one second partial injection during an injection cycle. In this context, at least one pre-injection and/or at least one post-injection are usually carried out in addition to a so-called main injection.
When controlling in such a manner, using two partial injections, a so-called minimum control interval must generally be maintained. This is used in order for the system to assume a defined initial state, so that unwanted injection-quantity fluctuations do not occur during the subsequent control. As a rule, the accuracy of one of the control events is of greater importance. If, for example, a post-injection used to regenerate a particle filter or an Nox catalyst is carried out, then this post-injection must be executed as accurately as possible with regard to its start of delivery and the amount.
If the minimum control interval between the two control events is not attained in this operating mode, then the main injection may have to be advanced. In the case of shifting the main injection, the result may be a different injection quantity, given the same delivery period. This is especially the case, when the injection quantity is a function of the start of delivery for the injection. This is particularly true for cam-driven injection systems, such as pump-nozzle units and/or solenoid-controlled distributor pumps.
Other variables characterizing the delivery period may be used in place of the delivery period. Examples of these include the triggering time of an actuator, and the injection period. The equivalent also holds true for the start of delivery. Other variables characterizing the start of delivery may be used in place of the start of delivery. Examples of these include the start of injection or the start of control.
The result of calculating the delivery period anew, using the new start of delivery, is a change in the interval between the two partial injections. Under unfavorable circumstances, it is necessary to correct the start of delivery again. This results in a highly time-consuming calculation of the control data for the main injection.
A similar problem occurs while carrying out a pre-injection and a main injection. In this case, the main injection has a higher priority. The case, in which the first injection has a higher priority and the second injection is shifted, may also occur.
The procedure of the present invention allows the new parameters, in particular the control (triggering) signals for the two injections, to be determined in a simple manner, in which case the minimum control interval is reliably maintained. In addition, the computational expenditure is markedly reduced.